CHEMICAL ENGINEERING

278 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

Comparing equations (iii) and (iv), then:

1

D^0

D

1

CTCA

{

CB

DAB

C

CC

DAC

C...

}

D

x^0 B

DAB

C

x^0 C

DAC

C...

wherex^0 B,x^0 CÐÐÐD

CB

CTCA

>

CC

CTCA

...

Dmole fraction ofB,C...in mixture ofB,C

For absorption of CO 2 from mixture with N 2 , the concentration driving force is:

CADCT 0. 3  0

 D 0. 3 CT

whereCTis the total molar concentration

The mass transfer rate for an areaADAN^0 ADCA

D

L

Ð

CT

CBm

ÐA

where: CBmis the log mean of 1ðCTand 0. 7 CT

or: CBmD

CT 0. 7 CT

ln

CT

0. 7 CT

D 0. 841 CTand:

CT

CBm

D 1. 189

Mass transfer rate,AN^0 AD 0. 3 CT

16 ð 10 ^6

L

1. 189 AD 5. 71 ð 10 ^6

CTA

L

D 0 .10 kmol/s

or:

CTA

L

D 0. 0175 ð 106 kmol/m^2.

For absorption of CO 2 from mixed stream, stream composition must be calculated.

100 moles stream 1!30 moles CO 2 70 moles N 2

100 moles stream 2!20 moles CO 2 50 moles N 2 30 moles H 2

200 moles mixture !50 moles CO 2 120 moles N 2 30 moles H 2

100 moles mixture !25 moles CO 2 60 moles N 2 15 moles H 2

x^0 N 2 D

60

75

D 0. 8 x^0 H 2 D

15

75

D 0. 2

Diffusivity of CO 2 in mixture is given by:

1

D^0

D

0. 8

16 ð 10 ^6

C

0. 2

35 ð 10 ^6

10 ^6

D^0

D

1

20

C

1

175

D 0 .0557 s/m^2

D^0 D 17. 9 ð 10 ^6 m^2 /s